Change pCodecParameters to pLocalCodecParameters in README.md

[Page-David]

Change pCodecParameters to pLocalCodecParameters in README.md

[leandromoreira]

Good catch.

[Page-David]

Hi, it is now that I finally find that simply replacing pLocalCodec with pLocalCodecParameters might not be a perfect solution. Instead, it might be better to firstly state that when we do the while loop to read AVPacket we need to distinguish video track from sound track. Also, when we create pCodecContext and call avcodec_parameters_to_context, we must use AVCodec and AVCodecParameters from the video track. Thus we need to "remember" them with pCodec etc. What do you think about?

Btw, could you please explain why do we need avformat_alloc_context() for *pFormatContext and why do we need av_frame_unref(pFrame);? So far, assigning NULL to *pFormatContext or remove av_frame_unref did not cause any problem for me. In chapter 2, AVFormatContext was assigned like AVFormatContext *input_format_context = NULL; why this time not avformat_alloc_context()?